The present invention relates to a manual film advance device used with a camera, and more particularly to a manual film advance device for use with a camera, such as a Blowny film camera, comprised of a manual film advance mechanism, as well as to a focal-plane shutter and a quick-return mirror which are charged in conjunction with the advancing action of the manual film advance device.
A manual film advance mechanism is generally used for a Blowny film camera, and a focal-plane shutter and a quick-return mirror are charged in conjunction with the film advance mechanism.
Such Blowny film camera is comprised of a film advance stop mechanism, a double film-advance inhibiting mechanism, and a film feed mechanism. The film advance stop mechanism converts into the rotation of a roller the extent to which a film is advanced by actuation of the film advance lever. When a predetermined amount of rotation (corresponding to the amount of rotation required to advance one frame of the film) has been achieved, the film advance stop mechanism prevents the film from being advanced in excess of one frame by stopping a film take-up spool even if the film advance lever has not been actuated all the way to the end of its range. After the film has been advanced one frame by the actuation of the film advance lever, the double film-advance inhibiting mechanism inhibits actuation of the film advance lever until a shutter is released. A rear cover of the camera body is closed after a start mark provided on the reverse side of a Blowny film loaded in the camera has been brought in alignment with an index marked on the body of the camera. The actuation of the film advance lever allows the film feed mechanism to advance the film from the start mark to a position one frame before where the first frame of the film would be placed at the aperture of the camera body, without actuating the focal plane shutter and the quick-return mirror.
If the film advance stop mechanism, the double film-advance inhibiting mechanism, and the film feed mechanism of a conventional Blowny film camera are all mechanically built from levers and gear trains, they become structurally complicated. Further, the number of constituent parts is also increased, thereby adding to the cost of the camera.
The angle through which the film advance lever is actuated is constant, whereas the diameter of the film take-up spool which is rotated in conjunction with the actuation of the film advance lever increases as the film is taken up. If the film advance inhibiting mechanism is operated by detecting the extent of advancement of film through use of only mechanical means, the film advance stop mechanism including a mechanism to detect the extent of advancement of film becomes further complicated. The precision of the parts affects the operation of the film advance stop mechanism, which in turn makes it impossible to ensure stable advancement of film.
The foregoing problem can be solved by electrically detecting the extent of advancement of film through use of a photo-interrupter or the like, and electrically controlling the film advance stop mechanism or the double film-advance inhibiting mechanism by utilization of a resultant electrical detection signal.
However, electrical control of the film advance stop mechanism or the double film-advance inhibiting mechanism requires a power supply, for which a battery is commonly used. As a matter of course, the battery has a life. If the battery is at the end of its life or if the battery is removed from the camera, the film advance stop mechanism or the double film-advance inhibiting mechanism does not work, thereby permitting wasteful advancement of film.